feat: implement user follow/unfollow functionality and thought retrieval by user

- Added follow and unfollow endpoints for users.
- Implemented logic to retrieve thoughts by a specific user.
- Updated user error handling to include cases for already following and not following.
- Created persistence layer for follow relationships.
- Enhanced user and thought schemas to support new features.
- Added tests for follow/unfollow endpoints and thought retrieval.
- Updated frontend to display thoughts and allow posting new thoughts.

thoughts-backend/models/src/schemas/user.rs

@@ -5,14 +5,14 @@ use crate::domains::user;
 
 #[derive(Serialize, ToSchema)]
 pub struct UserSchema {
-    pub id: u32,
+    pub id: i32,
     pub username: String,
 }
 
 impl From<user::Model> for UserSchema {
     fn from(user: user::Model) -> Self {
         Self {
-            id: user.id as u32,
+            id: user.id,
             username: user.username,
         }
     }